The present invention is generally directed to processes for the preparation of toner compositions, and more specifically the present invention is directed to toners and to processes for the preparation of encapsulated, especially colored encapsulated, toners wherein dispersing components are selected that, for example, enable passivation. Specifically, the present invention is directed to processes for the preparation of encapsulated toner compositions, especially encapsulated colored toners wherein block copolymers are selected as dispersants for the pigment particles, including colored pigments, and wherein the shells thereof can be obtained by interfacial polymerization, which shells are comprised of, for example, polyurethanes, polyesters, thermotropic liquid crystalline components as illustrated in U.S. Pat. No. 4,543,313, the disclosure of which is totally incorporated herein by reference, low melting polyesters, polyamides, and the like. In one embodiment of the present invention, the process comprises mixing pigment in the presence of a copolymer dispersant and an organic component; admixing the aformentioned mixture with shell monomers; dispersing the resulting mixture into an aqueous solution containing, for example, an optional emulsifier; and subsequently encapsulating the core comprised of pigment, dispersant and the liquid by accomplishing interfacial polymerization of the shell monomers with second shell monomers. In another embodiment of the present invention, particles are formed by dispersing a core component comprised of monomers, pigment, and a block copolymer dispersant into an aqueous solution containing an emulsifier, which particles can then be encapsulated by a polymeric shell as indicated herein. The toners illustrated herein can be prepared by an in situ process which comprises mixing pigment in the presence of a copolymer dispersant, and vinyl monomers; admixing the aforementioned mixture with shell monomers, preformed toner resins and radical initiators to form a homogeneous pigment dispersion comprised of both the shell and the core monomers, radical initiators, pigment, the preformed resins and the block copolymer dispersant; dispersing the mixture into an aqueous emulsifier solution to provide a suspension of pigmented droplets; subsequently encapsulating the core comprised of the pigment, the dispersant, the preformed resins and the vinyl monomers by accomplishing interfacial polymerization of the shell monomers with second shell monomers to obtain a stable suspension; heating the suspension to enable free radical suspension polymerization of the vinyl monomers to provide solid particles; and washing and drying the particles to yield the final toner product. The toner particles of an average volume diameter of from, for example, 5 to about 30 microns with narrow size distributions of from about 1.2 to 1.8 can be obtained, and classification is eliminated. The primary purpose of encapsulation is to passivate the pigment charging, that is the charging characteristics of the toner particles is ultimately controlled by that of the colorants, especially those exposed at the surfaces of the toner particles. Influence of the pigment charging can be prevented by encapsulation of various color particles with a common shell polymer of the desired charging properties. Therefore, developer charging, including triboelectric and admix characteristics, can be controlled and preselected with the process of the present invention. The copolymers selected as dispersants for the process of the present invention are nonionic dispersants and their adverse interference on the electirical properties of the toner composition is minimized and is less than when surfactant type ionic dispersants are utilized. The block dispersants possess an anchoring segment to enhance the attachment of the dispersant to the surface of a pigment particle and another segment, which is compatible with the selected toner resins, to provide steric stabilization. Block polymer dispersants selected for the processes of the present invention can thus provide superior dispersing, fluidization and antisettling performance compared to conventional surfactants in nonaqueous systems as detailed in Modern Paint and Coatings 1985, 9, 32; Journal of Coatings Technology 1986, 58, 71; and Coating Technology 1986, 58, 71, the disclosures of which are totally incorporated herein by reference. The dispersants illustrated herein can also be selected for the preparation of toner compositions comprised of resin particles and pigment particles, reference, for example, U.S. Pat. No. 4,289,672, the disclosure of which is totally incorporated herein by reference. Advantages of the process of the present invention are as illustrated herein and include the enablement of high loadings, for example, from about 7 to about 15 weight percent of pigment particles with minimal agglomerates within the toner particles to ensure optimized copy quality on paper and transparencies. Also, there is provided with the present invention a process for the preparation of various color toners from laboratory scale (less than 1.0 kilogram) to large scale toner production (up to several hundred kilograms). The toner compositions of the present invention are useful for permitting the development of images in electrostatographic systems, inclusive of electrostatic imaging and printing processes, including color processes.
As a result of a patentability search, there were selected the following U.S. patents. U.S. Pat. No. 3,974,078 discloses the use of block copolymers as dispersing agents, which agents were not functioning as pigment dispersants as is the situation with the copolymers of the present invention. More specifically, there is disclosed in the '078 patent the preparation of toner particles having two incompatible toner resins, one of which is soft and the other of which is tough, by using block copolymers as the dispersing or compatibility agent, see for example column 4, lines 35 to 64, and column 5, line 32. The copolymers enable the preparation of toner particles with such morphology that the soft polymer is encapsulated in a matrix of the tough polymers in a plurality of discrete domains. There are disclosed in U.S. Pat. No. 4,613,559 block copolymers as a steric stabilizer in the preparation of toners; and U.S. Pat. No. 4,148,741 discloses block copolymers as a stabilizer for the preparation of unencapsulated toners by suspension or bead polymerization. The block copolymers selected for the ' 741 process were not pigment dispersants but water soluble copolymer surfactants, typically the copolymers of ethylene oxide and propylene oxide, which were used to stabilize pigmented polymer particles with a size ranging from 200 to 600 microns during the suspension polymerization. Further, in U.S. Pat. No. 3,967,962 there are disclosed block copolymers as toner resins, and U.S. Pat. No. 4,263,389 discloses vinyl pyrrolidone polymers as dispersants.
There are disclosed in Konishiroku Japanese Publications 60/198554 A2, 60/198555 A2, and Canon Japanese Publication 61/65260 A2 heat fusible encapsulated toner compositions in which the shell of the encapsulated toner is prepared by an overcoating process involving the use of an organic solvent and polymeric materials of high melting points with a sufficient glass transition temperature to provide good blocking properties for these compositions. In contrast to the processes disclosed in the Japanese publications, the shells of the present invention can be prepared by interfacial polymerization in a simplified continuous one step process wherein the core and the shell of the toner are simultaneously formulated, which process therefore is of lower cost, that is from about 15 to about 40 percent less than the aforementioned prior art processes.
With further reference to the prior art, there is disclosed in Japanese Publication 61/56352 A2 heat fusible encapsulated toner compositions with a core prepared by in situ free radical polymerization with an epoxy-urea shell of a very high melting temperature. These toners do not ordinarily possess low melting properties, that is they usually cannot be heat fixed with fusers set at temperatures as low as 120.degree. C. In contrast, the toner compositions of the present invention can be used both in conventional heat fusing imaging systems wherein high melting materials with, for example, a softening point above 100.degree. C. are required necessitating fuser temperatures of up to 180.degree. C., and in low melt applications as the shell and the core can be formulated accordingly.
Additionally, there are disclosed in Japanese Publication 61/118758 A2, Japanese Publication 59/218460 A2, Japanese Publication 61/28957 A2, Japanese Publication 60/175057 A2, and Japanese Publication 60/166958 A2 heat fusible toner compositions prepared by suspension polymerization. Examples of patents illustrating colored photocapsule toners include U.S. Pat. Nos. 4,399,209; 4,482,624; 4,483,912 and 4,397,483. More specifically, the '483 patent illustrates encapsulated toner materials which have applications in very specific areas such as pressure sensitive recording paper. Capsules prepared for this application are usually coated on a substrate directly from the emulsion in which they are prepared and withstand with difficulties spray drying processes, a disadvantage alleviated with the toners prepared in accordance with the process of the present invention. Furthermore, these capsules contain an organic liquid in the core which, when used in a dry development system, could result in poor fix properties. Also, the range of particle sizes prepared by the aforementioned prior art process results in the formation of pressure sensitive recording particles which are usually not acceptable for electrostatographic development systems.
Moreover, there is described in U.S. Pat. No. 4,476,211, the disclosure of which is totally incorporated herein by reference, the preparation of electrostatographic toner materials with surface electroconductivity. Specifically, there is disclosed in the '211 patent a cold pressure fixable toner composition with polyamide, polyurea and other types of shell materials prepared by an interfacial polymerization process. The colorant selected for these compositions is generally comprised of a variety of dyes or pigments, and the core contains a polymeric material with a binder therein for retaining the colorant within the core and assisting in the fixing of the colorant onto the surface of a support medium. Examples of high boiling liquids selected for the process of the '211 patent include those boiling at temperatures higher than 180.degree. C. such as phthalic esters, phosphoric acid esters, and alkyl naphthalenes.
Furthermore, there are disclosed in U.S. Pat. No. 4,307,169 microcapsular electrostatic marking particles containing a pressure fixable core, and an encapsulating substance comprised of a pressure rupturable shell, wherein the shell, such as a polyamide, is formed by an interfacial polymerization. Additionally, there are disclosed in U.S. Pat. No. 4,407,922, pressure sensitive toner compositions obtained by interfacial polymerization processes, and comprised of a blend of two immiscible polymers selected from the group consisting of certain polymers as a hard component, and polyoctyldecylvinylether-co-maleic anhydride as a soft component.
Also, there are illustrated in U.S. Pat. No. 4,543,313, the disclosure of which is totally incorporated herein by reference, toner compositions comprised of resin particles selected from the group consisting of thermotropic liquid crystalline polycarbonates, copolycarbonates, polyurethanes, polyesters, and copolyesters; and pigment particles. The aforementioned thermotropic liquid crystalline polymers, especially the polyesters and the polyurethanes, are useful as shells for the toner compositions of the present invention. However, the toner compositions of the '313 patent are not encapsulated and are prepared by conventional processes, such as melt blending and jetting.
There is also disclosed in copending application U.S. Ser. No. 043,265, now abandoned the disclosure of which is totally incorporated herein by reference, toner compositions comprised of core components, and thereover a thermotropic liquid crystalline polymeric shell formulated by interfacial polymerization. Further, in this copending application there is described black or colored toner compositions comprised of a polymer core or polymer mixtures, and pigment particles encapsulated in a shell formulated by interfacial polymerization processes, which shell is selected from the group consisting of thermotropic liquid crystalline polyesters, polycarbonates, polyurethanes, copolycarbonates, and copolyesters, reference U.S. Pat. No. 4,543,313. Therefore, in one specific embodiment of the aforementioned copending application the toner compositions are comprised of a polymer core having dispersed therein as pigments components selected from the group consisting of black, cyan, magenta, yellow, red, magnetites, and mixtures thereof; and thereover a thermotropic liquid crystalline polymeric shell. Also, additive particles in an amount of from about 0.1 percent by weight to about 1 percent by weight, such as colloidal silicas, inclusive of Aerosils and/or metal salts, or metal salts of fatty acids, inclusive of zinc stearate can be added to the formulated encapsulated toner. Moreover, there can be incorporated into the toner compositions of the copending application charge enhancing additives in an amount of from about 1 percent to about 20 percent by weight to enable positively charged toner compositions, which additives include alkyl pyridinium halides, reference U.S. Pat. No. 4,298,672, the disclosure of which is totally incorporated herein by reference; sulfate and sulfonate compositions, reference U.S. Pat. No. 4,338,390, the disclosure of which is totally incorporated herein by reference; distearyl dimethyl ammonium methyl sulfate, reference U.S. Pat. No. 4,560,635, the disclosure of which is totally incorporated herein by reference; and the like. Furthermore, there are provided in accordance with the copending application processes for the preparation of toner compositions wherein the shell component is obtained by interfacial polymerization.
In one preferred specific embodiment of the aforesaid copending application, there are illustrated toner compositions comprised of a core of (1) a pre-polymerized styrene-n-butylmethacrylate copolymer with a glass transition temperature of about 55.degree. C. present in an amount of from about 1 percent by weight to about 30 percent by weight, and preferably from about 10 percent by weight to about 20 percent by weight, and an in situ polymerized styrene polymer present in an amount of from about 30 to about 50 percent by weight of the toner; and (2) a mixture of magnetite, from about 1 percent to about 60 percent by weight, and preferably from about 1 percent to about 30 percent by weight, and carbon black from about 2 percent to about 15 percent by weight, and preferably from about 3 to about 10 percent by weight, encapsulated with a polyester thermotropic liquid crystalline shell present in an amount of from about 10 percent to about 25 percent by weight. The resulting toner has a core/shell morphology with a shell thickness of from about 0.05 to about 1.0 micron. With further respect to the specific aforementioned compositions, there can be present in the core either carbon black or magnetite in an amount of from about 3 to about 8 percent, and from about 15 to about 20 percent, respectively.
Illustrated in a U.S. Pat. No. 4,758,506, the disclosure of which is totally incorporated herein by reference, are single component cold pressure fixable toner compositions, wherein the shell selected can be prepared by an interfacial polymerization process. A similar teaching is present in copending application U.S. patent Ser. No. 718,676 now abandoned relating to cold pressure fixable toners, the disclosure of which is totally incorporated herein by reference. In the aforementioned application, the core can be comprised of magnetite and a polyisobutylene of a specific molecular weight encapsulated in a polymeric shell material generated by an interfacial polymerization process.
Disclosed in copending application U.S. Ser. No. 416,071, are encapsulated toner compositions and processes thereof, and more specifically encapsulated toner compositions comprised of a core comprised of pigments, dyes or mixtures thereof, and a polymer; and wherein the core is encapsulated in a polyester shell with functional groups thereon derived from a diacid halide terminated polyester component. In this copending application some of the same polyester shells are utilized as selected for the encapsulated toners of the present invention, see the working Examples.
Primarily of background interest are the articles "Use of A-13 Black Polymers As Dispersants For Nonaqueous Coating Systems", H. L. Jakubauskus, Coating Technology, 58,71 1986; and "Improving Dispersion of Organic Pigments", T. Vernandukis, Modern Print and Coatings, 1985, 9 and 32, the disclosures of which are totally incorporated herein by reference.